An image sensor for capturing an image, includes: an array of pixel circuits, wherein each of the pixel circuits is for sensing a portion of the image, and generate a sample signal and a hold signal according to the portion of the image and a predetermined reset voltage respectively; and a transfer circuit, which is coupled to the array, and is for converting the sample signals and hold signals to corresponding digital sensing signals and corresponding digital reset signals respectively, to generate pixel signals respectively corresponding to the pixel circuits according to the digital sensing signals and the digital reset signals; wherein the transfer circuit converts the sample signal generated by one of the pixel circuits to the corresponding digital sensing signal and converts the hold signal generated by another one of the pixel circuits to the corresponding digital reset signal at least partially within a same period.